In the above-identified application, a system is described in which a drop in brake pipe pressure calling for a brake application initiates a pilot pressure. This pilot pressure is used to operate other valves pneumatically to effect braking.
During the initial part of an application of the bi-stable operator, air flows to atmosphere through the pilot exhaust choke. Similarly, during the initial stages of a release, air is feeding into the pilot chamber of the bi-stable operator at the same time as it is feeding to atmosphere via the pilot exhaust choke. This means that the pilot maintaining choke has to be small relative to the pilot exhaust choke. However, the pilot exhaust choke cannot be above a certain size otherwise pilot pressure would never reach a pressure within 11/2 p.s.i. of brake pipe pressure to cause the release valve to close.
As a result of the necessary relationship in sizes of these chokes, a limit is placed on the rate at which the pilot chamber can be exhausted and hence switch the piloted valves to their release position.